Investigators in the electric motor arts have been called upon to significantly expand motor technology from its somewhat static status of many decades. Improved motor performance particularly has been called for in such technical venues as computer design and secondary motorized systems carried by vehicles, for example, in the automotive and aircraft fields. With progress in these fields, classically designed electric motors, for example, utilizing brush-based commutation, have been found to be unacceptable or, at best, marginal performers.
From the time of its early formation, the computer industry has employed brushless d.c. motors for its magnetic memory systems. The electric motors initially utilized for these drives were relatively expensive and incorporated a variety of refinements particularly necessitated with the introduction of rotating disc memory. For example, detent or reluctance torque phenomena has been the subject of correction. The phenomena occurs as a consequence of the nature of motors configured with steel core stator poles and associated field windings performing in conjunction with permanent magnets. With such component combinations, without correction, during an excitation state of the motor windings which create motor drive, this detent torque will be additively and subtractively superimposed upon the operational characteristics of the motor output to distort the energized torque curve, increase ripple torque, reduce the minimum torque available for starting and, possibly develop instantaneous speed variations. Such instantaneous speed variations generally have not been correctable by electronics. Particularly over the recent past, the computer industry has called for very low profile motors capable of performing in conjunction with very small disc systems and at substantially elevated speeds.
Petersen, in U.S. Pat. No. 4,745,345, entitled xe2x80x9cD.C. Motor with Axially Disposed Working Flux Gapxe2x80x9d, issued May 17, 1988, describes a PM d.c. motor of a brushless variety employing a rotor-stator pole architecture wherein the working flux gap is disposed xe2x80x9caxiallyxe2x80x9d wherein the transfer of flux is parallel with the axis of rotation of the motor. This xe2x80x9caxialxe2x80x9d architecture further employs the use of field windings which are simply structured, being supported from stator pole core members, which, in turn, are mounted upon a magnetically permeable base. The windings positioned over the stator pole core members advantageously may be developed upon simple bobbins insertable over the upstanding pole core members. Such axial type motors have exhibited excellent dynamic performance and efficiency and, ideally, may be designed to assume very small and desirably variable configurations.
Petersen in U.S. Pat. No. 4,949,000, entitled xe2x80x9cD.C. Motorxe2x80x9d, issued Aug. 14, 1990 describes a d.c. motor for computer applications with an axial magnetic architecture wherein the axial forces which are induced by the permanent magnet based rotor are substantially eliminated through the employment of axially polarized rotor magnets in a shear form of flux transfer relationship with the steel core components of the stator poles. The dynamic tangentially directed vector force output (torque) of the resultant motor is highly regular or smooth lending such motor designs to numerous high level technological applications such as computer disc drives which require both design flexibility, volumetric efficiency, low audible noise, and a very smooth torque output.
Petersen et al, in U.S. Pat. No. 4,837,474 entitled xe2x80x9cD.C. Motorxe2x80x9d, issued Jun. 6, 1989, describes a brushless PM d.c. motor in which the permanent magnets thereof are provided as arcuate segments which rotate about a circular locus of core component defining pole assemblies. The paired permanent magnets are magnetized in a radial polar sense and interact without back iron in radial fashion with three core components of each pole assembly which include a centrally disposed core component extending within a channel between the magnet pairs and to adjacently inwardly and outwardly disposed core components also interacting with the permanent magnet radially disposed surface. With the arrangement, localized rotor balancing is achieved and, additionally, discrete or localized magnetic circuits are developed with respect to the association of each permanent magnet pair with the pole assembly.
Petersen in U.S. Pat. No. 5,659,217, issued Feb. 10, 1995 and entitled xe2x80x9cPermanent Magnet D.C. Motor Having Radially-Disposed Working Flux-Gapxe2x80x9d describes a PM d.c. brushless motor, which is producible at practical cost levels commensurate with the incorporation of the motors into products intended for the consumer marketplace. These motors exhibit a highly desirable heat dissipation characteristic and provide improved torque output in consequence of a relatively high ratio of the radius from the motor axis to its working gap with respect to the corresponding radius to the motors"" outer periphery. The torque performance is achieved with the design even though lower cost or, lower energy product permanent magnets may be employed with the motors. See also: Petersen, U.S. Pat. No. 5,874,796, issued Feb. 23, 1999.
Over the years of development of what may be referred to as the Petersen motor technology, greatly improved motor design flexibility has been realized. Designers of a broad variety of motor driven products including household implements and appliances, tools, pumps, fans and the like as well as more complex systems such as disc drives now are afforded a greatly expanded configuration flexibility utilizing the new brushless motor systems. No longer are such designers limited to the essentially xe2x80x9coff-the-shelfxe2x80x9d motor variety as listed in the catalogues of motor manufacturers. Now, motor designs may become components of and compliment the product itself in an expanded system design approach.
During the recent past, considerable interest has been manifested by motor designers in the utilization of magnetically xe2x80x9csoftxe2x80x9d processed ferromagnetic particles in conjunction with pressed powder technology as a substitute for the conventional laminar steel core components of motors. With this technology, the fine ferromagnetic particles, which are pressed together, are essentially mutually electrically insulated. So structured, when utilized as a motor core component, the product will exhibit very low eddy current loss which will represent a highly desirable feature, particularly as higher motor speeds and resultant core switching speeds are called for. As a further advantage, for example, in the control of cost, the pressed powder assemblies may be net shaped wherein many intermediate manufacturing steps and quality considerations are avoided. Also, tooling costs associated with this pressed powder fabrication are substantially lower as compared with the corresponding tooling required with typical laminated steel fabrication. The desirable molding approach provides a resultant magnetic particle structure that is 3-dimensional magnetically and avoids the difficulties encountered in the somewhat two-dimensional magnetic structure world of laminations. See generally U.S. Pat. No. 5,874,796 (supra).
The high promise of such pressed power components, however, currently is compromised by the unfortunate characteristic of the material in exhibiting relatively low permeability as contrasted at least with conventional laminar core systems. Thus the low permeability has called for 1xc2xd to 2 times as many ampere turn deriving windings. In order to simultaneously achieve acceptable field winding resistance values, the thickness of the winding wire must be increased such that the wire gauge calls for bulksome structures which, in turn, limit design flexibility. Indeed, earlier designers confronting the permeability values available with processed ferromagnetic particle technology will, as a first inclination, return to laminar structures. This is particularly true where control over the size of the motors is mandated as, for example, in connection with the formation of brushless d.c. motors employed with very miniaturized packaging . However, the disc drive industry now seeks such compact packaging in conjunction with high rotational speeds. In the latter regard, speed increases from around 7200 rpm to 15000 rpm and greater now are contemplated for disc drives which, in turn, must perform with motors the profile of which is measured in terms of a small number of millimeters. In general, lamination-based core structures cannot perform as satisfactorily at the higher core switching speeds involved, while particulate core-based structures have been hindered by the size restraints.
Petersen, in application for U.S. patent Ser. No. 09/728,236 filed Dec. 1, 2000 entitled xe2x80x9cd.c. PM Motor With a Stator Core Assembly Formed of Pressure Shaped Processed Ferromagnetic Particlesxe2x80x9d and assigned in common herewith addresses the use of processed ferromagnetic particles to provide a d.c. PM motor of a xe2x80x9cradialxe2x80x9d variety wherein flux transfer at the working gap as well as core component structuring is generally aligned with radii extending from the motor axis, Efficiency is achieved, inter alia, by enhancing the coupling of the applied field into the stator core structure through the utilization of transitions in levels between the radially disposed induction region and field winding support region of each core component.
The present invention is addressed to a d.c. PM motor as well as a corresponding generator which combines a radially directed magnetic flux transference at a working or functional gap with a pole or stator core structure wherein the stator cores are in a parallel relationship with the axis of the motor. When combined with the three dimensional structuring capabilities of pressure shaped processed, mutually insulated magnetically xe2x80x9csoftxe2x80x9d ferromagnetic particle stator core assembly structuring, important improvements in motor performance are realized in conjunction with a capability for reduction in weight, size and cost. In the latter regard, no more of the processed stator core assembly material is utilized beyond a given design tolerance factor for magnetic flux saturation.
A salient feature of the PM motor and generator structures hereunder resides in a broadened design flexibility accorded for essentially any given application of the technology. Motors application specific to a variety of implements, tools and appliances have been seen to replace, for example, the a.c. corded devices of the past. This replacement is with structures which are more powerful, capable of performing on battery power and yet are smaller and lighter. With respect to output torque achieved with the technology, motors configured according to the instant architecture will exhibit a ratio of radius-to-working gap (RRG) to the radius extending to the outer periphery or surface of the motor (RM) which is greater than about 0.6.
In one embodiment of the invention, the three dimensional capabilities for structuring the stator core assemblies are combined with a rotor structure having two radially outwardly disposed ring-shaped permanent magnets, each having a confronting magnetic surface adjacent oppositely disposed stator core component flux interaction surfaces to essentially double the rotor performance. By radially aligning the common polarities of the sequentially magnetized dual permanent magnets, a localized magnetic balance effect is achieved wherein the unbalance force vector evolved at one working gap is substantially cancelled by the unbalance force vector at the adjacent working gap. This feature permits a motor design wherein the internal region of the motor can be accessed from its side for a variety of purposes. For instance, the drive output of a rotor shaft may be tapped at the center of the motor to provide a side acting drive output. Such outputs can, for example, develop a linear actuator function. The attributes of the geometry and stator core materials as disclosed with respect to motor operation can equally be applied to generator operation.